Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

923
FXUS63 KLOT 150544
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1244 AM CDT Fri May 15 2026

.KEY MESSAGES...

- Chance for a period of showers late tonight into early Friday
  morning. Scattered strong storm chances then exist at times
  late Friday through this weekend.

- Better shot at widespread showers and storms, some possibly
  severe, Monday into Tuesday.

- Temperatures trend warmer through the weekend and into early
  next week.

&&

.DISCUSSION...
Issued at 215 PM CDT Thu May 14 2026

Surface high pressure centered over the region will keep
conditions quiet through this evening. A subtle short-wave and
push of mid-level WAA tonight will kick off a round of showers
tonight (after 04Z). With a lack of instability tonight the risk
for any thunderstorms is very low (less than 10%) and impacts
should be minimal. Showers should depart to the east mid-morning
Friday leaving the rest of the day dry with temperatures
peaking in the low to middle 70s. Winds on Friday will increase
as they become southerly, sustained winds of 15-20 mph are
expected through much of the day with wind gusts peaking around
25-30 mph. REFS shows a brief period of 20-40% probabilities for
greater than 30 mph gusts during the late morning with
diminishing probs through the afternoon as the pressure gradient
slacks off.

CAMs are in general agreement that another short-wave will
eject out of the southwest late Friday and pass through
otherwise zonal flow aloft. This feature will bring the next
chance for thunderstorms to the region late Friday into early
Saturday morning. Ahead of the short-wave surface dew points are
forecast to increase into the mid 50s which along with an EML
causing steepening mid-level lapse rates (7-8 C/km) will result
in elevated instability values of 1000-1500 J/kg. 0-6km shear
values of around 50 kts are also expected during this timeframe
as a 45-60kt jet streak passes over central WI. This will create
a parameter space capable of supporting a few marginally severe
elevated thunderstorms across the western half of the forecast
area with large hail the main threat, however, sporadic damaging
wind gusts are also possible.

A quasi stationary boundary is expected to set up somewhere
across the region Saturday which may provide the focus for
another round of thunderstorms Saturday afternoon/evening,
however, exactly where this boundary sets up will in part be
tied to how the early morning convection plays out. South of
this boundary low-level moisture transport will continue
throughout the day Saturday with dew points increase into the
low to mid 60s and temperatures warming into the mid to upper
70s resulting in 1000-1500 J/kg of surface based instability
which would support at least another round of stronger
thunderstorms. However, mid-level capping and the lack of a
stronger forcing mechanism may lead to more isolated storm
coverage.

A trough digging into the intermountain west later into the
weekend and early next week will result in prolonged period of
southwesterly flow bring more summer like conditions (high
temperatures in middle 80s to low 90s) to the region. Along with
the warmth there will be a chance for thunderstorms each day
through Tuesday as a series of short-waves move across the
region. Sunday the best storm chances will come during the
morning on the leading edge of an area of middle level WAA
before the area becomes capped during the afternoon. Monday the
region is forecast to be well into the warm sector with dew
points in the upper 60s and temps in the 80s leading to
impressive surface instability, however, the lack of a clear
forcing mechanism leads to low confidence in convective
evolution Monday. At this point the timeframe with the most
areal coverage of storms is late Tuesday as a well defined cold
front is forecast to swing across the forecast area.

Kaiser

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1244 AM CDT Fri May 15 2026

Forecast concerns for the terminals...

- Period of light showers/sprinkles overnight ending by
  daybreak.

- Breezy south-southwest winds Friday with gusts upwards of 25
  kts.

- Additional round of showers and thunderstorms Friday night
  into Saturday morning.


A shortwave disturbance continues to traverse across IA and
northern MO this evening which has allowed for some showers to
develop. While there were a couple of lightning strikes within
the showers earlier, recent radar trends continue to show the
cores struggling to maintain strength. Therefore, the threat for
thunder at the terminals tonight remains virtually zero. That
said, the narrow band of light showers/sprinkles that is
drifting over northern IL does look to pivot over the terminals
later tonight and may result in a brief (1-2 hour) period of
rain. However, given the very dry sub-cloud layer noted in AMDAR
soundings confidence is low as to how far east the
showers/sprinkles will get so have opted to just maintain the
PROB30s at the Chicago area sites for now.

Any showers that do make it into the Chicago sites should taper
by daybreak resulting in a mostly dry Friday for us. Though
those south of I-80 could see some lingering rain through mid-
morning as another cluster of showers drifts through. Otherwise,
expect winds to become south-southwest and increase in speed
Friday morning. Gusts look to generally top out in the 20-25 kt
range Friday, but if deeper mixing can be achieved then some
locally higher gusts may be realized. Wind gusts are expected to
ease Friday evening as the atmosphere decouples with winds
becoming more southerly. However, there is a chance for
directions to vary from a 170-190 direction during the evening
hours.

Heading into Friday evening, another shortwave disturbance will
be pivoting across the Midwest and should result in another
round of showers and thunderstorms developing in IA. While
guidance remains in good agreement that these showers/storms
will persist into northern IL and northwest IN Friday night,
confidence on their overall intensity and coverage is somewhat
low. The reason is because the cluster of showers and storms may
be outrunning some of the better instability and moisture which
could allow them to weak with eastward extent. Regardless,
confidence is high enough to warrant the introduction of SHRA
with a PROB30 for TSRA in the 30-hour TAFs. Note that a formal
mention was left out of the 24-hour TAFs since rain looks to
hold off until right at the tail end of the period, but will
need to add it with the 12z TAF issuance.

VFR conditions are expected to prevail through the entire TAF
period.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory from 8 AM this morning to 7 PM CDT this
     evening for the IL and IN nearshore waters.

&&

$$

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